The computer mouse used for navigation on personal computers has evolved significantly since its invention by Douglas Engelbart, as shown in his U.S. Pat. No. 3,541,541.
The modern computer mouse is not mechanical, but optical. An optical mouse is described in U.S. Pat. No. 6,433,780 by Gordon et al, incorporated herein by reference. An optical mouse has a motion sensor with a light source which illuminates the surface the mouse rests upon. Optical elements focus an image of this surface on an image sensor. Processing electronics connected to the image sensor sense motion by correlating successive images from the image sensor, performing a correlation of successive images with different offsets in X and Y directions, and finding the maximum of the correlation surface.
Dust contamination of the optical elements reduces the effectiveness of the optical mouse by creating a fixed pattern in sensed images. While this is less of a problem with mice which use conventional imaging, since such dust is out of the focal plane, it is of particular concern in optical mice using interference imaging. The fixed pattern created by dust leaves a peak in the correlation function at zero displacement. For small motions, this central peak at zero motion in the correlation function distorts the algorithms which find the sub-pixel resolution peak.